Protein kinases, the largest family of human enzymes, encompass well over 500 proteins. Kinases play critical roles in signaling pathways controlling fundamental cellular processes such as proliferation, differentiation, and death (apoptosis). Abnormal kinase activity has been implicated in a wide range of diseases, including multiple cancers and autoimmune and inflammatory diseases. The multifaceted role of kinases in key cell signaling pathways provides a significant opportunity to identify novel drugs targeting kinases and signaling pathways. Diseases mediated by receptor kinase activity include, but are not limited to, diseases characterized in part by abnormal levels of cell proliferation (i.e. tumor growth), programmed cell death (apoptosis), cell migration and invasion, and angiogenesis associated with tumor growth.
Because kinases are key regulators they are ideal drug design targets. Inhibitors of kinases are among the most important classes of pharmaceutical compounds known. Highly specific, cell-permeable inhibitors of one or more individual kinases are useful for the treatment of various kinase-implicated diseases. Kinase inhibiting compounds are additionally useful for the systematic investigation of the cellular function of one or more kinases, and thus, provide valuable tools for the identification of various kinases of therapeutic interest.
Bruton's Tyrosine Kinase (Btk) is a member of the Tec family of tyrosine kinases, and is a critical regulator of early B-cell development as well as mature B-cell activation, signaling and survival.
B-cell signaling through the B-cell receptor (BCR) leads to a wide range of biological outputs, which in turn depend on the developmental stage of the B-cell. The magnitude and duration of BCR signals must be precisely regulated. Aberrant BCR-mediated signaling can cause disregulated B-cell proliferation and/or the formation of pathogenic auto-antibodies leading to multiple autoimmune and/or inflammatory diseases. Mutation of Btk in humans results in X-linked agammaglobulinaemia (XLA). This disease is associated with the impaired maturation of B-cells, diminished immunoglobulin production, comprised T-cell-independent immune responses and marked attenuation of the sustained calcium sign upon BCR stimulation.
Evidence for the role of Btk in autoimmune and/or inflammatory disease has been established in Btk-deficient mouse models. For example, in standard murine preclinical models of systemic lupus erythematosus (SLE), Btk deficiency has been shown to result in a marked amelioration of disease progression. Moreover, Btk deficient mice are also resistant to developing collagen-induced arthritis and are less susceptible to Staphylococcus-induced arthritis.
A large body of evidence supports the role of B-cells and the humoral immune system in the pathogenesis of autoimmune and/or inflammatory diseases. Protein-based therapeutics (such as Rituxan) developed to deplete B-cells, represent an important approach to the treatment of a number of autoimmune and/or inflammatory diseases. Because of Btk's role in B-cell activation, inhibitors of Btk are useful as inhibitors of B-cell mediated pathogenic activity (such as autoantibody production).
Btk is also expressed in mast cells and monocytes and has been shown to be important for the function of these cells. For example, Btk deficiency in mice is associated with impaired IgE-mediated mast cell activation (marked diminution of TNFα and other inflammatory cytokine release), and greatly reduced TNFα production by activated monocytes.
Thus, inhibition of Btk activity is useful for the treatment of autoimmune and/or inflammatory diseases such as: SLE, rheumatoid arthritis, multiple vasculitides, idiopathic thrombocytopenic purpura (ITP), myasthenia gravis, and asthma. In addition, Btk has been reported to play a role in apoptosis, thus inhibition of Btk activity is useful for the treatment of B-cell lymphoma and leukemia.
Agents capable of inhibiting Btk kinase activity, are highly desirable for the treatment of a variety of diseases, including cancer, an autoimmune and/or inflammatory disease, or an acute inflammatory reaction. Specific, cell-penetrating, small molecule, non-peptide antagonists of Btk are of particular value for such therapies. Such compounds are also useful for the systematic investigation of the cellular function of Btk, and thus, are valuable research tools for the identification of cell signalling proteins of therapeutic interest.
The present invention fulfills this need, and provides further related advantages.